Starch selective oxidation

D-Glucaric acid, directly produced by nitric oxidation of glucose or starch, is usually isolated as its 1,4-lactone. The technical barrier to its large-scale production mainly includes development of an efficient and selective oxidation technology to eliminate the need for nitric acid as the oxidant. Because it represents a tetrahydroxy-adipic acid, D-glucaric acid is of similar utility as adipic acid for the generation of polyesters and polyamides (see later in this chapter). 

Levulinic acid is formed by the treatment of six-carbon sugar carbohydrates from starch or lignocellulosics with acids, or by add treatment plus a reductive step of five-carbon sugars derived from hemicellulose. Levulinic add can serve as a building block for the synthesis of many derivatives of interest may be the selective oxidation to succinic and acrylic add. [i-Acetylacrylic add could be used in the production of new acrylate polymers. 

Dinitrogen tetraoxide (N2O4) selectively oxidizes some of the primary hydroxyl groups. One solvent-based process involves selective oxidation of starch with N204 in the presence of oxygen119 to give a product with 75% uronic acid units. Co-builders for use with zeolites have been produced by oxidation and hydrolysis of starch with a gas phase of N02/N204 in a fluidized bed.120... 

Aldehyde starches are prepared by treatment with periodic acid/periodate ions, which selectively oxidize the adjacent hydroxyl groups on carbon atoms 2 and 3 to aldehyde groups. Dialdehyde starch can react with cellulose by forming covalent hemiacetal and acetal bonds.40 It is primarily used as a wet strength agent in the production of tissue and other sanitary grades. 

Selective oxidation of primary hydroxyl groups can be achieved with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and hypobromite or hypochlorite at pH 10.5-11. A 98% selectivity was observed for starch, and selectivity of over 90% for inulin [113]. 

Recently, the oxidative formation of the Ce group in carbohydrates has became a strong focus of investigation, since when it is applied to the starch molecule, superabsorbing material based on renewable resources can be produced. Therefore, the development of new catalytic methods for the selective oxidation of terminal alcohols Cg by applying simple and cheap oxidants such as hydrogen peroxide still remains challenging. 

Oxidation of secondary hydroxyl groups at C-2 and C-3 leads to acyclic dialde-hydes and dicarboxylic derivatives. Selective oxidation of primary hydroxyl groups is more difficult, but can be achieved by stoichiometric as well as catalytic methods. Nitric acid oxidizes monosaccharides into aldaric acids. Oxidation of cellulose or starch by nitrogen dioxide (N2O4) yields 6-carboxy starch and 6-carboxycellulose respectively. Subsequent hydrolysis under well-controlled conditions (0.5-2 M HCl at 150 °C) of these materials yields o-glucuronic acid (o-GlcAp) [12]. 

Several investigations have been carried out to modify starch catalytically with the aim of obtaining specific hydrophilic properties. For example, selective oxidation of the hydroxymethyl groups of starch molecules leads to polycarboxylic adds, which can be used as adsorbers in diapers (nappies). A suitable catalyst for the synthesis of... 

Oxammonium salts such as 81 are new and powerful oxidizing agents for the selective oxidation of alcohols to aldehydes or ketones. 28 Such salts can be generated catalytically from small amounts of a nitro-xide in the presence of a secondary oxidation procedure, either chemical or electrochemical,. 29 or with two equivalents of acid and 2 equivalents of a nitroxide. When 81 was mixed with acetylenic alcohol 82 in dichloromethane, aldehyde 83 was isolated in 93% yield. The reaction can be monitored as the initial yellow slurry changes to a white slurry and the presence of unreacted oxidant can be checked with starch. 3l It is not necessary to use anhydrous conditions, and it was discovered that the rate of reaction was enhanced by the presence of silica gel. This reagent is compatible for the mild oxidation of many alcohols, including aliphatic primary and secondary as well as allylic and benzylic alcohols. 

FIGURE 5.20 Preparation of a dialdehyde polysaccharide by the selective oxidation of starch Adapted from Ref. [107] with the permission from Elsevier limited. 

Due to its large availability and low cost, native starch has been used for a long time in the preparation of different end-products. To obtain specific properties, native starch has to be chemically or enzymatically modified. Because native starch is an insoluble, partially crystallized solid polymer, chemical modifications are difficult to achieve and require the use of soluble catalysts. We have achieved two catalytic modifications of native starch (i) selective oxidation to obtain carboxyl and carbonyl functions, thus making starch more hydrophilic (8), and (ii) telomerisation of butadiene with the hydroxyl groups of the glucoside units, thus providing more hydrophobic material (8,9). 

Current industrial methods of chemical modification of starch by oxidation are based mainly on oxidizing agents like NaOCl to introduce carboxyl groups or NaI04 to obtain aldehyde functions. 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO) was applied in combination with NaOCl/NaBr or with peroxide reagents (JO) to oxidise selectively primary hydroxyl groups in polysaccharides. While these oxidations are chemically efficient they lead to inorganic wastes. 

In conclusion, the selective oxidation of native starch by hydrogen peroxide in the presence of metallophthalocyanine catalysts provided hydrophilic materials which, from primary tests, look promising for their incorporation in paints and cosmetics. These catalysts are not expensive, readily available at industrial scale and employed in very low amounts. The catalytic system was very flexible because by simple modifications of the reaction conditions it was possible to prepare oxidized starches with the desired level of carboxyl and carbonyl functions that are suitable for different applications. No wastes were formed because the process did not involve any acids, bases or buffer solutions. 

Ammonia decomposition over Fe, Cu, Ag, Au, and Pt Hydrolysis of starch to glucose catalyzed by acids Mixture of coal gas and air makes a platinum wire white hot Measurements on the rate of H2O2 decomposition Selective oxidation of ethanol to acetic acid over platinum Comprehensive paper on the H2 + O2 reaction on platinum foils, including reaction rates, deactivation, reactivation, and poisoning Definition of catalysis, catalyst, and catalytic force First quantitative analysis of reaction rates Systematic studies on the concentration dependence of reaction rates First concise monograph on chemical kinetics Definition of order of reaction Arrhenius equation k = u exp (-Ea/RT)... 

The pH must be kept at 7.0—7.2 for this method to be quantitative and to give a stable end poiut. This condition is easily met by addition of soHd sodium bicarbonate to neutralize the HI formed. With starch as iudicator and an appropriate standardized iodine solution, this method is appHcable to both concentrated and dilute (to ca 50 ppm) hydraziue solutious. The iodiue solutiou is best standardized usiug mouohydraziuium sulfate or sodium thiosulfate. Using an iodide-selective electrode, low levels down to the ppb range are detectable (see Electro analytical techniques) (141,142). Potassium iodate (143,144), bromate (145), and permanganate (146) have also been employed as oxidants. 

Modified starches may be acid-modified, oxidized, or heat-treated. Acid-modified (thin-boiling) starches are used mainly in textiles as warp sizes and fabric finishes. Here they increase yam strength and abrasion resistance and improve weaving efficiency. Tbin-boiHng starches also have selected appHcations in paper and laundry starch preparations. 

Primary and secondary amines and amides are first chlorinated at nitrogen by the chlorine released by the gradually decomposing calcium hypochlorite. Excess chlorine gas is then selectively reduced in the TLC layer by gaseous formaldehyde. The reactive chloramines produced in the chromatogram zones then oxidize iodide to iodine, which reacts with the starch to yield an intense blue iodine-starch inclusion complex. 

The water-soluble iron tetrasulfophthalocyanine (FePcS) complex, which is cheap and available on an industrial scale, was also a very active and selective catalyst for the oxidation reaction. Starches of different origin (potatoes, rice, wheat, com) were oxidized by H202 following two operating modes, viz. oxidation in aqueous suspension and oxidation by incipient wetness. 

Oxygen difluoride may be analyzed by GC, GC/MS, IR, and NMR methods. The compound may be identified by GC/MS, the characteristic mass ions are 54, 38 and 35. The compound can be measured quantitatively by wet methods based on its strong oxidizing ability (see Reactions). It liberates I2 from an acidified solution of potassium iodide and the liberated I2 can be measured by iodometric titration using Na2S20s titrant and starch indicator. Alternatively, the compound may he treated with a measured amount of excess NaOH and the unreacted excess NaOH measured hy titrating against a standard solution of HCl. Also, the fluoride ion, F, may he measured by fluoride selective electrode. 

Oxidation of carbohydrates is probably the most efficient heterogeneously-catalyzed process since very high yield and selectivity are reported for reactions over solid catalysts. Despite important recent advances, the conversion of carbohydrates to HMF still requires further investigations. For reactions, in water, the yield of HMF is still too low due to the significant formation of side products. Today, several procedures for the conversion of monosaccharides, disaccharides, oligosaccharides, and starch in water into high value added materials are available. With cellulose, its heterogeneously-catalyzed conversion into useful products... 

Of the myriad of modified starch systems tested, ranging from simple enzymically dextrinized starches to covalently attached amino acids and peptides onto dextrinized and/or oxidized (hypochlorite or periodate) corn starch bases, two polymers were selected as holding promise. The first system was a low dextrose equivalent (DE 5.7) enzyme-modified corn starch. The second starch-based polymer developed was a periodate-oxidized, amylase-dextrinized, covalently-attached phenylalanine glycoamine. 

Oxidized Starch Production Methods. Multiple methodologies were utilized to produce the corn starch products of hypochlorite and periodate oxidation. Ultimately only three of these procedures were selected as yielding functional product and will, therefore, be the only methods to be outlined here. 

Covalent linkage of amino acid, peptide or protein moieties onto the hydrolyzed and/or oxidized polymers (Control and Oxidized starches) was examined for its ability to improve the potential for microregion lipophilicity within the carbohydrate polymer. Proteinaceous materials are often strongly surface active (39) and may, if carefully selected, contribute positively to wall material characteristics. This selection process was carried-out using maltodextrins (DE 10 and/or 25) as the carbohydrate framework and various amino acid-derived materials as the function-altering accessory, ranging from gelatin and casein proteins to simple amino acids. 

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